The basic patent for establishing a negative pressure, air flow enclosure for an asbestos removal work area within a building is U.S. Pat. No. 4,604,111. This patent discloses a particulate contamination control method and filtration device, and a system for establishing a negative pressure, air flow enclosure. This patent addresses the serious dangers associated with persons breathing particulate contaminated air. The invention is useful for protecting the outside environment and the individuals working in a highly contaminated area such as occurs when asbestos coatings and other asbestos materials are removed inside a building structure.
Asbestos fibers fall into the generic classification of hazardous particulate and are a well known carcinogenic hazard to humans and animals. Typical environmental standards refer to fibers that are 5 microns or greater in length with an aspect ratio of 3 to 1 or greater. The average asbestos fiber is about 0.1 micron in diameter. It is now accepted that the thinner fibers are the most dangerous threat to human health. The asbestos fibers, in particular those that are thinner and shorter, remain airborne for considerable lengths of time and contaminate large volumes of air to form a substantial hazard to the environment and to the persons working or living in the area.
U.S. Pat. No. 4,604,111 provides a system and method of containing, lowering, and essentially eliminating the danger of asbestos escaping from an asbestos removal work area in a building where asbestos fibers are generated at extremely high levels. Airborne asbestos fibers are prevented from being released to the outside environment during an unforseen accident such as a leak through a damaged film barrier and by a flap seal arrangement which seals the inlet to the contaminated work area through which workers pass to gain entrance to and exit from the work area.
The flap seal arrangement is formed in the plastic wall defining the work area and is utilized in the doorways of the decontamination chamber, as well as the waste chamber for removed asbestos, equipment and the like. As disclosed in the '111 patent, a sheet of plastic film is sealed across a door frame with an opening cut through the film. The preferred opening is disclosed as a two foot by five foot opening about a foot off the floor, and the plastic film is polyethylene, plasticized polyvinyl chloride or the like. The "flap seal" is larger in all dimensions than the opening of the same film, is attached to the door frame above the opening and hangs over the full length of the opening such that air and the workers may pass into the work area through the opening, pushing the flap inwardly. The configuration is such that once the air flow ceases and negative air pressure is lost in the enclosure, the flap falls into place and air is prevented from escaping in the opposite direction to the environment outside of the work room.
Many similar plastic film "flap seal" arrangements are in use today. These include various double and triple flap arrangements that permit workers to pass into and out of the work area while at the same time providing an air inlet opening sufficient to allow substantial air flow through the flap arrangement and into the work area and which automatically close upon loss of negative air pressure in the work area.
In these various flaps seal arrangements in accordance with the '111 patent, the flap seal arrangement is designed to seal the air inlet into the contaminated work area. This arrangement has proven to be very effective in preventing escape of asbestos fibers in the event of loss of negative air pressure. However, other factors need to be considered in designing a combined entrance and exit from the contaminated work area. For example, it is often very difficult to pass through these entrance/exitways in the event of fire or the like.
In U.S. Pat. No. 4,818,970, a fire condition detection and control system for air moving and filtering units is disclosed. The fire condition detection and control system is for use with air moving and filtering units such as those disclosed in the '111 patent. The fire condition detection and control system includes one or more remote fire condition detection units, which sense heat or smoke and, upon such sensing, transmit a signal indicative of an alarm condition to one or more air moving and filtering units located within the containment enclosure. The transmission is by wireless radio frequency transmission and/or a wired transmission line or cable. The air moving and filtering unit detects the alarm condition and disconnects power to the blower motor of the air moving and filtering unit. The receiver and control circuitry may be integral with the air moving and filtering unit, or may be part of a separate control unit that plugs into conventional air moving and filtering units.